The present invention relates to an improved process for regenerating ion exchange materials, and more specifically, to a process for carrying this out using a countercurrent technique.
A recently allowed U.S. patent application Ser. No. 07/369,238 to Gerhard K. Kunz filed Jun. 22, 1989 entitled PROCESS AND APPARATUS FOR ION EXCHANGERS, PARTICULARLY FOR REGENERATION AFTER SOFTENING AND DEMINERALIZATION OF AQUEOUS SOLUTIONS which describes the Kunz countercurrent regeneration process is incorporated herein by reference. A Kunz counterpart application has issued in the Republic of South Africa as 89/4669 and is also incorporated herein by reference. The Kunz countercurrent regeneration process describes the regeneration of a non constrained bed of ion exchange materials in a countercurrent fashion by admitting the regenerating solution using alternating pulse flow and non flow conditions. During the non flow period, the bed of ion exchange material which is lifted during the up flow pulse period is allowed to settle. In this process, the pulse flow velocities and volumes, and the settle times (non flow period) between pulses are carefully defined. This process is currently being successfully employed commercially under the tradename Impulse.TM. by Impulse Regeneration Services of Hatboro, Pa. for the regeneration of water softeners, a process during which the regeneration uses a solution of NaCl to remove divalent cations from cation exchange materials.
The use of the Kunz countercurrent process for demineralization requires the regeneration of cation exchange materials back to the hydrogen form and anion exchange materials back to the hydroxide forth. Regeneration of commercially available cation exchange material with a mineral acid such as HCl proceeds very much as the cation regeneration with solutions of NaCl. Regeneration of commercially available anion exchange materials however can only be accomplished by a significant increase in the settle time between pulses.
In the Kunz process, the density difference between the ion exchange material and the regenerating solution is the major factor that determines the settle time that is required between pulses to insure essentially complete resettling of the bed. As taught by Kunz, essentially complete resettling of the bed is necessary to ensure optimum regeneration efficiencies. The smaller the difference in the densities between the ion exchange material and regenerating solution, the greater the settle time required in the Kunz process to settle the ion exchange materials back to essentially their initial position. In the case of softening, typical density differences using commercially available cation resins and typical regenerating salt solutions are in the range of 0.13 g/cm.sup.3 to 0.17 g/cm.sup.3. For example, as practiced commercially, the Kunz process used to regenerate a softener has a settle time of 15 seconds. Total regeneration time as commercially practiced requires 4 to 5 hours.
The regeneration of commercially available anion exchange materials involves significantly smaller density differences, typically 0.05 g/cm.sup.3 to 0.08 g/cm.sup.3 between normally used anion exchange materials and their regeneration solutions. Experimental use of the Kunz process for regenerating such anion resins results in extended settle times in order to achieve essentially complete re-settling of the bed. Settle times in the order of 45 seconds have been observed resulting in a total regeneration time in excess of 7 hours. Thus, although the Kunz regeneration process can be made to work with both the cation and the anion exchange materials required for demineralization, the total regeneration time of this process becomes quite long, thereby reducing its commercial viability.
It has now been discovered that the Kunz process may be improved by significantly reducing the settle time between pulses by using a down flow pulse (or down flow) of liquid in the opposite direction to the up flow or pulse. This reduction in settle time dramatically reduces the total time required for regeneration under the Kunz process while maintaining the basic regeneration chemical utilization advantages of the Kunz process.